1. Field
The present disclosure relates to an apparatus for generating extreme ultraviolet light.
2. Description of the Related Art
Recently, lithography, which uses extreme ultraviolet light for microfabrication of semiconductor devices, has been proposed. Lithography is a technique which reduces and projects light or beams onto a silicon substrate through a mask having a circuit pattern drawn thereon, and exposes a photoresist material to light so as to form an electronic circuit.
The minimal processing dimensions of the circuit formed by optical lithography depend on the wavelength of a light source. Therefore, the wavelength of the light source needs to be shortened in an optical lithography process for fabricating semiconductor devices with reduced dimensions. Extreme ultraviolet (EUV) light sources may be suitably used as the next generation lithography light sources. EUV light has a wavelength of approximately 1 to 100 nm. Since extreme ultraviolet light has high absorption with respect to all materials, a reflective optical system is used rather than a transmissive optical system such as a lens.
For example, EUV light may be generated by deposition of, e.g., laser, energy into a source element to create ionized plasma. In detail, laser produced plasma (LPP), i.e., using the radiation of laser beam, and discharge produced plasma (DPP), i.e., using the discharge of a gas and driven by a pulse power technique, may include interaction of a laser beam with a droplet of source element, e.g., tin (Sn), to evaporate and superheat the source element to generate plasma that emits photons toward a reflective mirror to generate the EUV light.